Comparison of the BACGene Listeria spp. Real Time PCR and BAX® System 24E Genus Listeria PCR Methods for the Detection of Genus Listeria in Food and Environmental Samples from Two Dairy Production Facilities
Daniel R. DeMarco, Colin O'Malley, Jennifer Willig, Douglas Marshall, Roger Hooi and Anita Gerung
Abstract
Introduction
A large dairy product manufacturer expressed interest in an alternate PCR method for the detection of Genus Listeria in their environmental and product testing program due to recurring false-positive detections and high levels of environmental Genus Listeria positives in the recent past.
Purpose
Our objective was to compare the performance of two PCR based methods for Genus Listeria detection.
Methods
BAX® System 24E and BACGene® Listeria species were used to test 244 environmental samples and 33 product samples collected from two working production plants in different locations. Environmental samples were collected using a novel split sampling device in an attempt to provide as close to equivalent input samples as possible for both methods. Culture confirmation of presumptive positives was performed if either of two sister samples was presumptive positive by either test method. For some negative sister samples additional culture work was performed (secondary enrichments and additional platings) in an attempt to recover any Listeria present.
Results
No presumptive positives were seen for any product samples by either method. For environmental samples BAX gave 50 presumptive positives of which 48 were confirmed by culture. The BACGene method gave 40 presumptive positives all of which were confirmed by culture. Out of 56 positive samples, 34 samples agreed
between methods. Of the 20 samples that disagreed, 14 were BAX positive/BACGene negative and 6 were the reverse. Chi-square analysis of the total number of positives by each method showed no statistically significant difference in performance at (p <0.05, p-value = 0.05876).
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